The really sad part is that it wouldn't take a whole lot to restore it to that sort of condition...
Obviously there's some things that can't be done, mostly concerning the stones, but getting in there with some weed-eaters, some rakes, lopping sheers, and mayhaps a chainsaw or two could make the Grove look like people care again.
It's abandoned because it's been allowed to become abandoned.
I for one say it's time to reclaim the Grove. Find some contacts at the Forest Preserve, find out what we need to make everything happen, and then get it handled.
As much as I love the Grove, I'm sick of seeing it in it's forgotten state, and after seeing these pics and reminding myself what it looked like in the mid-90s when I visited it the first time, I think we should reclaim it now, and keep it that way.